Triplet-type objective lens



May 13, 1969 P. RUBEN 3,443,863

TRIPLET-TYPE OBJECTIVE LENS Filed Jan. 23. 1967 I II 111 l J I R R2 R3R4 R5 R6 PAUL L. RUBEN INVENTOR.

Y m 719M529)?- ATTORNEYS United States Patent 0 US. Cl. 350-226 6 ClaimsABSTRACT OF THE DISCLOSURE A photographic objective of the simpletriplet type is disclosed which is well corrected for very high relativeapertures, and is particularly suited for use in motion picture cameras.

This invention relates to improvements in photographic objectives of thesimple triplet type having a high relative aperture.

An object of this invention is to provide an inexpensive simple triplettype of photographic objective having a relative aperture of f/2.7 whichis well corrected for spherical and chromatic aberrations, coma,astigmatism, flatness of field, and is particularly suited for use onmotion picture cameras.

Further objects and advantages will be found in the details ofconstruction disclosed in the accompanying examples and drawing.

The present invention comprises triplet objectives having two outepgsitive elements and an inner negative biconcave element. The innernegative elements of the triplets of this invention are positioned closeto the front positive elements, and in most of the embodiments disclosedbelow the front two elements have contacting edges. The thin airspacereduces spherical aberrations. The use of contacting edges provides easyand precise mounting, which is particularly critical when the airspacesare thin. Thin airspaces are sensitive to slight changes of thicknessand consequently require close tolerance in mounting.

The drawing shows a cross sectional view of an objective embodying theinvention with the long conjugate on the left.

The objective in the drawing comprises three airspaced simple lenses,designated I, II and III. The outer two lenses I and III are positiveelements, and the inner lens II is a negative biconcave element. Thediaphragm is located in front of lens I.

Numerical data for constructing six embodiments of photographicobjectives according to the invention as outlined above is given in thefollowing examples in which the lens elements are numbered from front torear, N is the index of refraction of the lens elements for the D line,V is the index of dispersion, and R, T and S refer respectively to theradii of curvature of the lens surfaces, the

thicknesses of the lens elements and the airspaces between the elements,numbered by subscript from front to rear.

EXAMPLE 1 Equivalent Focal Length=100 mm. 172.?

Lens ND V Radil (mm.) Thlcknesses and spacings (mm.)

Stop

S =31.2 R1=50.4 I 1. 61 58.8 T1=28.6

S 1.61 R3: 46.6 II 1. 62 36. 6 T;=7.61

Sz=6.84 R5=143 III l. 61 58.8 T3=20.2

EXAMPLE 2 Equivalent Focal Length 100 mm. f/2.7

Lens ND V Radil (mm.) Thicknesses and spacings (mm.)

Stop

S 19.9 R1=52.1 I 1. 61 68. 6 T =26.4

S1=1.57 Rz= -51.0 II 1. 61 37.0 T1=7.15

S1=2.72 R5=270 III l. 61 58. 6 T;=19.3

EXAMPLE 3 Equivalent Focal Length=l00 mm. ]/2.7

Lens ND V Radii (mm.) Thicknesses and S paclngs (mm.)

Sto

p So=20.8

R =43.1 I 1.49 57.4 T,=21.5

S1= 1.57 Rr= 58.0 II 1.57 36. 6 Tg=7.14

S;=4.14 Rs=94.6 III 1.61 58. 8 T =20.0

In the above three examples the inner negative element is in edgecontact with both positive elements for easy mounting.

The elements in Examples 1 and 2 are all glass, but in the Example 3embodiment of this invention, the front two components are formed fromplastic and the third component is formed from glass. The use ofplastic-glass combinations in triplets is disclosed in US. Patent3,194,- 116 in which the negative element is formed from a copolymer ofacrylonitrile and styrene having an index of ,4 simple negativebiconcave lens element, the lens elements having substantially thefollowing characteristics and spatial relations in which the lenselements are numbered from the front, N is the index of refraction forthe D line, V is the index of dispersion, and R, T and S referrespecrefraction N about 1.56 and an index of dispersion about 5 tivelyto the radii of curvature of the lens surfaces, the 37. To balance theelfect of thermal expansion, one of the axial thicknesses of the lenselements, and the axial spacpositive elements can be formed from aplastic, preferably ings between the lens elements, numbered bysubscript methyl methacrylate having an index of refraction N from frontto rear: about 1.49 and an index of dispersion about 57.

EXAMPLE 4 Lens ND V Radll Thlcknesses and Equivalent Focal Length= 100mm. f/2.7 spacings R =.504F Lens v (mm') I 1.61 58.8 59F T1=.286FS1=.016F II 1.62 36.6 A661? T;=.076F

Rt=39.2 R4=.466F I 1.61 58.6 T1=12.7 R 3F 20 III 1.61 58.8 i T;=.202F90,5 R|=.654F II 1.61 37. o T1=6.15

R4=39.2 2. A photographic objective of the simple triplet type III R 4having an equivalent focal length F and comprising two F outer simplepositive biconvex lens elements and an inner simple negative biconcavelens element, the lens elements EXAMPLE 5 having substantially thefollowing characteristics and Equivalent Focal Length: 100 m. spatialrelations in which the lens elementsare numbered fromthe gloat, 51 1sftlzle 1nde x of redfrfict lon fgrSthefDr ine, 1s e m ex 0 rspersion, anan re e Lens ND v (mm') Efiiffffi respectively to the radii of curvatureof the lens surfaces, the axial thicknesses of the lens elements, andthe axial stop spacings between the lens elements, numbered by subscriptR 518 from front to rear:

1 30 I 1. 75 50.6 R,= 281 T =29.0

R= 80 0 S1=2-25 Lens N n V Radli Thicknesses and II 1.72 29.3 R 45 2'T,=5.o0 spacings 40 R1=.521F III 1. 75 50.6 R 1403 Tg=12.6 I u 1.61 58.6R'= -756F T1='264F RFD-71.7 R 51oF S1=.016F II 1.61 37.0 P T;=.072F Theabove two Examples 4 and 5 have only the front SF'OWF two components inedge contact. In Example 5, as well I s= -70 as Example 6 following, allelements are formed from I I TF'lgaF glasses having high indices ofrefraction N which reduces spherical aberratioihin the Exampleembodiment 3 A p g p objective of the i pl p e typ of the mventlon noneg l l are m Contact. having an equivalent focal length F and comprisingtwo outer simple positive biconvex lens elements and an inner EquivalentLengihfloo f/2-7 simple negative biconcave lens element, the lenselements having substantially the following characteristics and Lens v(mm') spatial relations in which the lens elements are numbered from thefront, N is the index of refraction for the D line, stop V is the indexof dispersion, and R, T and S refer respecs=14.s tively to the radii ofcurvature of the lens surfaces, the I 1.75 524 13:28.9 axial thicknessesof the lens elements, and the axial spac- R1=313 ings between the lenselements, numbered by subscript from front to rear: II 1. 72 29. aT;=5.0

rat-46.3 R: 140 SFHJ Lens N V Radlt Thlcknesses and III 1.75 52.4T;=12.6 spacings I 1. 49 57.4 RPAMF T1=.215F Although the invention hasbeen described in consider- S 0161, able detail with reference tocertain preferred embodi- R==.5s0F ments thereof, it will be understoodthat variations and n RG33 modifications can be elfected withoutdeparting from the R 9461, spirit and scope of the invention asdescribed hereinabove. III 1.61 58.8 h T =.200F

What is claimed is: 1. A photographic objective of the simple triplettype having equivalmt focal length F and p ing two 4. A photographicobjective of the simple triplet type outer simple positive biconvex lenselements and an inner 75 having an equivalent focal length F andcomprising two outer simple positive lens elements and an inner simplenegative biconcave lens element, the lens elements having substantiallythe following characteristics and spatial relations in which the lenselements are numbered from the front, N is the index of refraction forthe D line, V is the indexof dispersion, and R, T and S referrespectively to the radii of curvature of the lens surfaces, the axialthicknesses of the lens elements, and the axial spacings between thelens elements, numbered by subscript from front to rear:

5. A photographic objective of the simple triplet type 7 Lens ND RadiiThlcknesses and i spacings R =.5l6F I 1.75 50. 6 T|=.290F

Rg=2.81F

S,=.023F Ra=.800F I1 1. 72 29. 3 T=.050F

s,=.097F Rs=L4OF III 1. 75 50.6 'I.-,=.126F

6. A photograph1c ob ective of the simple triplet type having anequivalent focal length F and comprising two outer simple positivebiconvex lens elements and an inner simple negative biconcave lenselement, the lens elements having substantially the followingcharacteristics and spatial relations in which the lens elements arenumbered from the front, N is the index of refraction for the D line, Vis the index of dispersion, and R, T and S refer respectively to theradii of curvature of the lens surfaces, the

axial thicknesses of the lens elements, and the axial spacings betweenthe lens elements, numbered by subscript from front to rear:

having an equivalent focal length F and comprising two outer simplepositive biconvex lens elements and an inner Lens ND V Ra i ic krgesisfssand simple negative biconcave lens elements, the lens elements p ghaving substantially the following characteristics and 30 RFJUF spatialrelations in which the lens elements are numbered I R2: BF i=-289F fromthe front, N is the index of refraction for the D R s line, V is theindex of dispersion, and R, T and S refer n 29,3 TFMOF respectively tothe radii of curvature of the lens surfaces, R4=.463F 2 mm the axialthicknesses of the lens elements, and the axial 35 h R5=1.40F

III 1. is 52. 4 T;=.126F spacings between the lens elements, numbered bysubscript from front to rear:

References Cited UNITED STATES PATENTS 3,359,057 12/1967 Ackroyd 350-226DAVID SCHONBERG, Primary Examiner. RONALD I. STERN, Assistant Examiner.US. Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,443,863 May 13, 1969 ram. L. Ruben It is certified that error appearsin the above identified patent and that said Letters Patent are herebycorrected as shown below:

Column line .l43F should read R 4 Signed and sealed this 14th day ofApril I970.

(SEAL) Attest:

WILLIAM E. SCHUYLER, JR.

Commissioner of Patents Edward M. Fletcher, Jr.

Attesting Officer

